1. Field of the Invention
The present invention relates to an autonomous electricity production and conditioning system for an aircraft, including:                a rotary shaft;        a compressor mounted integral with the rotary shaft;        a power turbine capable of rotating the rotary shaft;        a cold expansion turbine rotated by the rotary shaft and supplied with a compressed gas from the compressor.        
Such a system is in particular intended to be used on a civilian aircraft, such as a passenger and/or freight airplane, or on any other flying vehicle.
2. Brief Discussion of the Prior Art
In aircrafts, it is necessary to have a system performing temperature, pressure and hygrometry conditioning functions of the aircraft. Such a system is generally designated as an “Environmental Control System” or “ECS.”
Such a system comprises a compressor and a cold turbine mounted on a same shaft. The compressor is generally fed with air from an engine withdrawal or from an air turbogenerator. The compressed air, after cooling and drying, is expanded in the cold turbine to produce the frigories necessary for conditioning of the aircraft.
Generally, the aircraft is also provided with an air turbogenerator (ATG, also called APU, or “auxiliary power unit”) intended to produce electricity and air for the aircraft's needs. This turbogenerator includes a power turbine supplied with combustion gases produced in a combustion chamber independent of the engine(s) of the apparatus. A compressor is mounted on the shaft of the power turbine to allow pressurized air production on the ground, and to supply the combustion chamber.
The presence of these two systems on a same aircraft has drawbacks in terms of weight and bulk.
To offset this problem, US 2010/0170262 describes an autonomous system of the aforementioned type, in which a power turbine supplied by a combustion chamber, a compressor, and a cold expansion turbine intended to produce a cold gas for the environmental control system are mounted on a same shaft.
To feed the compressor, a withdrawal is done in a low-pressure zone of a propulsion engine of the aircraft. This withdrawal provides hot air leaving the engine to supply the intake of the compressor. This hot air is generally conveyed to the compressor by passing through a heat exchanger to condition it at the right temperature.
Such a system reduces the onboard weight and volume, while preserving the necessary functionalities for the aircraft. Thus, when the propulsion engines are turned off, the combustion chamber can be activated to rotate the power turbine, the compressor and the cold turbine so as to allow conditioning of the cabin. Furthermore, when an alternator is driven by the shaft supporting the turbines and the compressor, the rotation of the alternator creates electricity necessary for the needs of the aircraft, in the absence of primary electricity production provided by the alternators coupled to the engines of the aircraft.
Once the engines are started, they supply the conditioning system(s) with air.
Such an assembly is not fully satisfactory, in particular on civilian airplanes. In fact, all of the gas provided at the intake of the compressor comes from the engine.
When the engine is off, or when it is not working correctly, the compressor must suction air through the immobile blades and the structure of the engine, which significantly increases the pressure loss to be overcome. The compressor must therefore be oversized, which increases its bulk, mass and consumption. Furthermore, the engine air withdrawal intended for the compressor of the conditioning system directly influences the thermodynamic cycle of the engine, which increases the consumption thereof.
Furthermore, the existing standards on civilian airplanes require a maximum usage temperature of the engine gases that is restrictive. This temperature is 204° C. However, the temperature of the withdrawn gases is much higher, for example in the vicinity of 260° C. These gases must therefore be cooled by an air-air exchanger before being conveyed into the aircraft, which causes significant energy consumption.
The sizing of the system, and in particular of the air intakes in the engine, is complex to perform, and requires compromises between optimal thermodynamic use of the engine and the conditioning system.